Plants which are grown on agricultural land or general households are often infected with plant viruses, and as a result, the value of commodities, production amounts and appearance, and the like, as an agricultural crop, may be remarkably decreased. Plant virus diseases may cause serious damage to important crops such as grains, vegetables, and fruit trees. Viruses which have invaded plant cells proliferate entirely relying on the metabolisms of the host plants. For this reason, it is difficult to specifically inhibit only the proliferation of the viruses whilst maintaining the normal metabolic pathways in plants. Therefore, plant virus diseases have been diseases which are difficult to be controlled.
Several control agents against plant virus diseases have been proposed. For example, Patent Literature 1 discloses a composition which contains antibacterial antibiotics such as neomycin sulfate and organic acids such as ascorbic acid, and states that the composition is capable of inhibiting plant diseases. In addition, in Patent Literature 1, the ascorbic acid is used for playing a role in assisting the antibacterial substances.
However, anti-plant virus agents which have been proposed hitherto have problems such as in the productivities thereof, in actual inhibitive effects against plant diseases, and safety in animals and plants, and most of them have not been put to practical use. In addition, while anti-plant virus agents which exhibit preventive effects have been proposed, very few anti-plant virus agents which exhibit therapeutic effects have been proposed.
On the other hand, ascorbic acid (vitamin C) or ascorbic acid derivatives have been used for medicines, cosmetics, food, and feedstuffs, and the like. In addition, the use thereof in the prevention of blemishes or freckles, and the like, from a suntan, and the use thereof as a hair growth agent have been proposed (refer to Patent Literatures 2 and 3). However, use of ascorbic acid derivatives for controlling plant diseases is not known.